<md-sidenav-container>
<md-sidenav #sidenav>
  <app-sidebar></app-sidebar>
</md-sidenav>
  <div class="site">
    <header>
      <app-header></app-header>
    </header>
    <main>
       <button (click)="sidenav.open()">打开侧边栏</button>
    </main>
    <footer>
      <app-footer></app-footer>
    </footer>
  </div>
</md-sidenav-container>
